Volume 3 2013

Photo: Evan Larson
Water Resources Research

Learning From Trees

Climate Variability Data Found in Tree Rings

By Marie Zhuikov

New technologies provide inspiration for some research projects, and some are a result of studies. For Evan Larson, assistant professor of geography at the University of Wisconsin-Platteville, inspiration came in the form of a bike ride.

“I was riding through the Platteville countryside, and I saw all these beautiful old oak trees,” said Larson, who also co-directs UW-Platteville’s Tree-Ring, Earth and Environmental Sciences (TREES) Laboratory (www3.uwplatt.edu/trees). “I realized the area had a lot of trees that have lingered on the landscape since before European settlement, and that those trees could tell us the history of the climate in this region.”

Larson and Christopher Underwood, an adjunct research faculty member at the TREES Lab, successfully submitted a proposal to the University of Wisconsin Water Resources Institute that was awarded two years of funding. Their project, Establishing the Long-Term Range of Variability in Drought Conditions for Southwest Wisconsin, involves taking core samples from more than 400 ancient oak trees throughout Wisconsin’s Driftless Region. In this first comprehensive tree coring study for the region, researchers will analyze the ring-width patterns within the cores for signs of long-term variability in rainfall and climate conditions to lay the foundation for similar efforts across the state.

“Trees are excellent recorders of their environment,” Larson said. “Wide rings indicate years of good growth while narrow rings represent stressful times. Using these patterns of growth, we can expand our perspective on climate beyond what instrumental records can tell us, moving further into the past to build a more complete picture of the range of potential drought conditions we may face as a region.”

Sara Allen, a UW-Platteville geography and history double major, will help spearhead the project as a post-bachelor research fellow, along with six to eight undergraduate students.

“Southwestern Wisconsin is an agricultural area, and the drought that affected crop production last year had a negative impact on the farmers throughout the region. Looking into historical drought patterns can help us better prepare for possible water deficits in the future,” Allen said. “This project will give me the opportunity to move into a mentoring role after I graduate in May. I’m excited to teach undergraduates about the applications of tree-ring research and help prepare the next wave of enthusiastic dendrochronologists.”

Dendrochronologists study the growth rings of trees with a variety of tools. For this project, researchers will take samples from living trees with increment borers—essentially a hollow drill bit, turned by hand, that removes a pencil-width piece of wood from the tree. Drilling into the tree, Larson said, is akin to taking a blood sample from a person and does not cause the tree lasting damage.

Although Larson’s bike ride helped pinpoint the location of some trees, the researchers need help from the public to find others.

“What makes the Driftless Area of southwestern Wisconsin so beautiful are the rolling hills and hidden valleys that were once covered by oak savannas,” Larson said. “But this beauty also makes it difficult to conduct a thorough inventory of the area for old trees. There are simply too many hidden hollows and valleys for us to explore.”

Landowners in southwestern Wisconsin who have oak trees they suspect may be hundreds of years old on their property are invited to contact Larson if they would like their trees considered for the project.

“There is something about oak trees that resonates with people, and this often leads to curiosity about their ages,” said Larson. “Although we cannot always determine the exact age of a tree because of rot or the precision needed to cross the very center of a trunk with an increment borer, we can provide a good estimate in most cases.”

The researchers hope that in exchange for permission to sample the rings of old oaks, they can offer property owners a glimpse into the environmental history of their land.

Larson can be reached at (608) 342-6139 or larsonev@uwplatt.edu.

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